On October 1st, 2010, the Bing web crawler will come out of beta. At that time the crawler will also be rebranded from msnbot to bingbot.
The updated user agent will be:
Mozilla/5.0 (compatible; bingbot/2.0 +http://www.bing.com/bingbot.htm)
The HTTP header From field will also change as shown below:
The bingbot will still honor robot.txt directives written for msnbot so no change is required to your robots.txt file(s). More information on the Robots Exclusion Protocol of bingbot and how to report issues can be found at the Bing Webmaster Blog.